Thread: Varnish skinning in the tin

Oldblock,

The reason for the skin is that oxygen has got to the varnish/oil etc. In a full tin there is very little oxygen between the top of the brew and the top of the can so skinning is minimal.

If you can reduce the amount of oxygen available to react with the brew then skinning will be reduced.

Like you say decanting into smaller containers is one way, another way is to displace the brew with something inert such as glass marbles which will sink to the bottom and force the brew closer to the top. Thus reducing the available oxygen and therefore the skinning.

- Wood Borer

Marbles? Marbles?
Dearie me I have major problems. I have two lots of marbles the first lot are in a tin in my workshop; the others are are somewhere in my head but I cant find them.

I bought the first lot to do just what you suggest four years ago. I put them aside ready for the next time I was decanting and promptly forgot they were there and what they were for.

I'm at the bottom of my current can of varnish and grovelling around among bits of broken skin, picking bits off the work with the brush etc, telling myself it will all come off in the sanding and by the time I get to the top coat I will have started a fresh can.

Thanks WB.
Now where did I put those marbles.

Ray

G'day.

I have found the marbels trick to work well.
I found good sized bags of marbels at The Warehouse toy section for 99cents a bag.
When the container is all used up, you can just chuck them all out or give them a wash with whatever solvent works with the finish you are storing & recycle them.

I've been known to store paint tins upside down so the skin forms on the bottom and isn't in the way when you turn it up the right way, this works okay, but if you can find your marbles (good luck old timer ) that sounds like a better proposition

You can also get 'dry nitrogen' in a spray-pack can from resin suppliers like Barnes Products & possibly Daystar, here in Sydney. Moisture & Oxygen make all sorts of finishes go 'off' - although with a pure spirit based shellac I would think that a bit more metho would fix the problem.

Hi bsrlee,
In the past I have found that if I invert the tin the contents tend not to "skin over".

Rodger

Nitrogen in the can, marbles, upside down, none of this will stop the process once it started.
Varnish, dries with different chemical process depending on the blend of oil and drying oils in it, but we can say that the process is kick started by oxygen that brakes the double links and frees hydrogen. We have then formation of hidroperoxides or cyclic peroxides depending on oil used, that in time will produce free radicals that by themselves accelerate the auto oxidation process. No amount of reducing the oxygen in the can will stop the varnish from become one solid block of jelly, it may slow it down a bit, that is all. If that would be so easy, than the film formed on the surface should be enough to isolate the rest of the tin yet we all know this does not happen.

We can do two things though. First filter the content of the can after finish using it with a fine cloth, and to place the remaining varnish in a clean container, to eliminate any solid clumps that contain the seed for further drying the varnish, second the main one is to put the tin in the fridge. The oxidation process is highly dependent on light and temperature, if we keep our varnish in a tin and not a plastic transparent bottle and if we place it in our beer fridge in the shed, it will stay fresh and flowing for a very long time. Remember that the cloth used for filtration, is a candidate for self-combustion, use the usual precautions.

Well well well!

So endeth another quest. From now on I will stop trying to be smart by buying large cans to save money and frigging about decanting into smaller ones.

Much obliged Marc

Hi Oldblock, you can still buy large cans, I do. And you can still decant them in smaller cans so that you isolate the oxidation process. Just remember to filter the lumps out once you finish painting, and never dip the brush in your main container unless you plan to use it all for that job. The brusch is riddled with dry little bits of varnish and when you squeeze the brush to the sides you add lots of air bubble to the mix and this two will start the chain reaction in your big tin.
Try the following: find two small bottles, or plastic pills container or similar. Take a sample from the bottom of your tin, the one with lumps and marbels at the bottom, well on the way of becomeing a solid block. Take two equal ammounts and place them in your two containers. Put one next to your varnish tin in the usual place, put the other in the fridge, and forget about them for a month. Have a look at the results, if still similar wait for another month. Change should be faster in summer.

I was told by and aged painter who used to us a lot of varnishes and he always used to put the lid over the tin and before closing it he put it to the cars exaust(with the motor running lol) and filled the tin with exaust fumes and then closed it and he never had a skinning prob so if you try it you may have the problem solved of removing oxygen from your tins................

Cheers Tasman.